The present communication environment is rapidly evolving, transcending boundaries of regions and countries and fields of wired/wireless communication, and this movement is bound to continue its course into the future. In this trend, the communication environment is prepared to integrally provide various information required by users as well as images and voices in a real-time. Digital television systems processing the moving image into digital data, transmitting the digital data in real-time, and mobile communication networks receiving the digital data for displaying the moving image being transmitted in real-time in personal terminals are implemented and popularized.
FIG. 1 is a block diagram illustrating a structure of an apparatus for coding a moving image according to conventional technologies.
Both inter prediction 120 and intra prediction 121 are performed with an input image 110. A switch 140 selects a better prediction method between the inter prediction 120 and intra prediction 121. A difference image between the input image 110 and a prediction image obtained from either the inter prediction 120 or intra prediction 121 is entropy coded 160 via discrete cosine transform (DCT) 130 and quantization 150. Also, the difference image reconstructed in this apparatus for coding the moving image through inverse quantization 151 and inverse DCT 131 is summated with the prediction image obtained through the inter prediction 120 or intra prediction 121, thereby obtaining a reconstructed image. This reconstructed image is used for the intra prediction 121, and a de-blocking filtering 170 is performed on the reconstructed image is used for the inter prediction 120.
In such commercialization process, development of a moving image compression technology functions as a core factor since the moving image compression technology performs quantization with respect to analog image signals, processes special digital processes such as variable length coding, includes the processed signals in digital information and transmits the digital information, and decodes the transmitted digital information received in a terminal, thereby transmitting/receiving more abundant information at a faster transmission speed. To enhance efficiency of the moving image compression, intra prediction mode and inter prediction mode are provided and implemented. In particular, the intra prediction mode is a prediction method exclusively using information within an image frame, without using temporal correlation. As precise prediction is performed, redundancy with an original block to be coded is increased, and an amount of data is minimized by removing redundancy from the original block when actually transmitting, thereby enhancing the compression.
The H.264 coding standard may improve coding efficiency by using coding tools different from conventional arts. The intra prediction coding, which is one of newly used coding tools, predicts a coding target block by using spatial correlation when coding an intra block, and exclusively codes a residual signal between a predicted value and an actual pixel value.
In such intra prediction, there are intra prediction of a 4×4 block unit, intra prediction of an 8×8 block unit, and intra prediction of a 16×16 block unit. In the intra prediction of the 4×4 block unit and the intra prediction of the 8×8 block unit, nine prediction modes are available. In the intra prediction of the 16×16 block unit, four prediction modes are used. In all intra predictions, difference signals and the information regarding the above prediction mode used in the prediction are coded together.
In the case the difference between the predicted value and the actual pixel value is small, it is possible to code a high quality image with identical bits or it is also possible to process coding with lower bits. Therefore, an apparatus for coding an image which is capable of generating prediction values with small differences to the actual pixel value, and an apparatus for decoding which is capable of decoding the coded images generated from the above apparatus are required.